Sexual Selection and Parental Investment

Sexual selection and Parental investment

In no species does every male or female have the same opportunities to mate with any chosen partner. Darwin (1874) noted that it is the deer with the biggest antlers and the peacock with the most impressive plumage that gets his pick of the females. Darwin used the concept of sexual selection to account for these findings. Within this model there are two components; firstly intrasexual selection whereby same-sex competition for preferential access to mates occurs, this, in the most part, takes place between males. Intrasexual competition does not always have to be through direct physical competition it may be, for example through competition for status. Thus, high status/ strong males gain superior access to the ‘best’ mates. The second component of sexual selection is intersexual selection. This form of selection involves the preferential choosing of certain members of the opposite sex as mates. Throughout the majority of species, it is usually the females who engage in this form of selection. This can be explained in terms of the varying amount of parental investment that males and females have to place when raising children.

Trivers (1972) defines parental investment as:

“Any investment that increases the offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring.” Trivers (1972, p67)

For males, this investment can involve purely fertilisation of an egg; however, for females it involves pregnancy, breastfeeding and care of the child until adulthood. As women have a higher investment in the bearing and bringing up of a child, it is clear that they would be likely more discriminating in their choice of mate than would males.

As children are such an extensive investment to the mother, acquiring resources to support her and her offspring is of paramount importance (Cashdan, 1996). Females therefore value signals of ability to provide resources such as the financial capacity, ambition and industriousness of potential mates more than males do (Buss, 1989). In addition to resources, females of most species and ancestral women would have needed protection for herself and her children and would therefore seek a male willing and able to fight off any threats to them.

Evolutionary psychology therefore holds that females attraction towards males and subsequent decision to mate with them is based upon traits shown by men that signal their ability to provide for and protect her and her offspring as well as supplying good genetic qualities to pass on to their children.

Cashdan claims that women have acute evaluative mechanisms for good condition in a mate and accordingly, many male features that are viewed as attractive are associated with “good genes”. One example is fluctuating asymmetry which is the measure of asymmetry

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